This invention relates to electronic interconnect devices, such as wires and terminals, which have enhanced solderability characteristics, and to a method for forming such devices.
Both lead wires and hook-up wires are soldered to other wires or to other connectors to create electrical connections as required for a wide variety of purposes. The bond made by the soldering, both mechanically and electrically secure. Interconnect problems are costly and dangerous. For example, in the military, interconnect problems may be the largest single source of electronic equipment down time.
Solderable wire generally is formed by tin plating on a copper substrate core. Ideally, the tin plate reacts with the tin-lead alloy of the solder to create a bond during the soldering process. However, either prior to the soldering or during the soldering, to avoid problems such as circuit failure, must be process the tin interacts with the core metal to form interface compounds such as Cu.sub.6 Sn.sub.5 and Cu.sub.3 Sn which are not capable of forming a secure bond with the solder. This results in an unstable connection being formed. These interface compounds will form over time at room temperature or more quickly when heat is applied to the wire during soldering or annealing. Additionally, tin is permeable to oxygen resulting in substrate oxides, which like the other interface compounds, weaken the mechanical bond between the solder and the connector.
One solution to provide a solderable wire is to plate the wire core with silver rather than tin. The silver does not oxidize or react with the core to form interface compounds and is left free to create a strong bond with the solder. However, silver is expensive to use.
Accordingly, it is a purpose of this invention to provide an improved solderable wire which forms stable mechanical and electrical bonds.
Yet a further purpose of this invention is to provide such a wire which has an enhanced shelf life.
Another purpose of this invention is to provide such a wire which is economical to produce.